Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

OSPF, Frame Relay and /32


consider following small frame relay network:


| Se0


/ \

DLCI 102 / \ DLCI 103

[r2] [r3]

Configuration of frame relay is done entierly on main serial interface on all routers (i.e. sub-interfaces are not used). All interfaces are in the same /24 subnet. OSPF is configured on these interfaces as point-to-multipoint (alternatively as 'broadcast'). Once adjacency is formed, spoke routers will install /32 routes for each other spoke via hub router. All works fine, each spoke can ping other spoke without a problem.

For many years I just took for granted that such setup works, because it just seems to be natural to install /32 in order to get connectivity between spokes. But today I started to wonder where such behaviour is specified. I went through several RFC, digged in Cisco and Juniper documentation but couldn't find anything on the topic.

Does anyone know some document, which specifies/formalises installation of /32 routes in scenarios where two routers are on the same subnet but not OSPF neighbors? Is this universal behaviour or have somebody experienced different with other manufacturers?


Re: OSPF, Frame Relay and /32

This isn't documented anyplace that I know of.... I poked through the RFC, and it's not there, that I can find. In fact, I don't think point-to-multipoint is documented at all.

In general, this is universal behavior. I know Cisco, Juniper, Redback, and all the other vendors I've checked do this. You'll note that these implementations were all done by a small number of folks who actually all know each other, so the implementations are very similar, in the way they act, even in areas outside the official RFCs.